Heat exchanger systems are used in a large variety of industrial, commercial, and consumer applications. Aluminum has been used successfully for many years in the construction of many types of heat exchanger systems due to its physical properties. Aluminum is lightweight, has high thermal conductivity, good corrosion resistance, and further has a relatively low cost. Aluminum is also widely used in industrial heat exchanger systems because of its compatibility with ammonia and halocarbons, which are commonly used with same.
Evaporator heat exchangers, such as those used in industrial refrigeration systems, are fed with refrigerants in a number of different ways. One popular method for controlling the flow of refrigerant to the evaporator is by direct, or “dry,” expansion. This method employs an automatic expansion valve which modulates so as to maintain a preset, constant amount of heat at the exit of the heat exchanger. Larger direct expansion evaporators will generally be constructed with two or more parallel refrigerant circuits. Each of these multiple parallel circuits must be supplied with equal amounts of refrigerant from the exit of the expansion valve. To do this, a refrigerant distributor is used to deliver equal mass flow to each of the refrigerant circuits. The refrigerant distributor assembly includes a conical body with an inlet at one end of the conical body and multiple outlet ports which are equally spaced around the perimeter of the base of the body. A small diameter conduit, called a distributor “lead” or conduit, fluidly connects each port in the distributor to each refrigerant circuit in the heat exchanger.
Traditionally, aluminum tube, direct expansion heat exchangers have necessarily utilized aluminum distributor bodies and distributor leads. Because of the difficulties associated with welding small diameter aluminum tubing, these aluminum distributor assemblies and leads have been inherently prone to cracking and leaks, especially in the region surrounding the welding zone located at either end of the respective leads. Ammonia refrigerant leaks, of course, present risks of fire and explosions and immediate health risks to persons nearby. Halocarbon refrigerant leaks present serious environmental problems that may lead to civil liabilities for the user thereof.
In view of the problems associated with the prior art devices and practices utilized heretofore, there has been a long felt need for an improved aluminum heat exchanger system. The prior art is replete with numerous examples of couplers for coupling conduits fabricated from different metals. For example, U.S. Pat. No. 6,886,629 teaches the use of a steel header applied to an aluminum plate heat exchanger. However, the welding method disclosed in that patent does not appear to be useful for a refrigerant distributor assembly having multiple small-diameter tubular leads, such as those used in a direct expansion evaporator heat exchanger. Additionally, mating dissimilar metal tubes using explosion welding or roll bonding is well known in the art. For example, U.S. Pat. No. 6,843,509, which is incorporated by reference herein, teaches an explosively welded coupler for joining a steel or stainless steel conduit to an aluminum conduit when those conduits have similar outer diameter dimensions. The particular teachings of that patent, however, do not appear to be useful for solving the several problems identified above, and more specifically where a small diameter stainless steel distributor lead must be mated with a larger diameter aluminum heat exchanger tube.
A metal tubular heat exchanger system connected to a fluid distributor fabricated from a dissimilar metal, and which avoids the shortcomings attendant with the prior art devices and practices utilized heretofore, is the subject matter of the present application.